Dunno...none of my BM 59s or my italian bolts are modified for them.
None of my Italian Garand bolts were modified either. I built up an "all correct" Berertta Garand (if a VAR barrel is correct, than it is all correct) and this match Garand with a BMR receiver
I used a GI bolt on the match rifle, but used the Italian trigger group
I am glad I purchased a whole bunch of Beretta parts, as those parts were cheap, and good. Total drop in for GI Garand receivers, and high quality. At the time, I had buds who looked down on the Italian parts, but you know, Beretta has been making rifles since the 1600's, and is still making firearms, so they ought to know what they are doing.
Military weapons go through rebuilds, it is very possible that the rifles that came in, at some point in time, the Italians started modifying the bolts with a spring. Those that had not made it in, were left alone.
Sort of like the secret recalls on Takata airbags. If the airbag blew , and did not kill the passenger or driver, the car manufacturer replaced the airbag.